Process of extracting metals from their ores.



W. E. GREENAWALT.

PROCESS OF EXTRACTING METALS FROM THEIR ORES.

APPLICATION FILED SEPT. 30. 1912.

1,179,522. Patented Apr. 18, 1916.

M I INVENTOR.

WITNESSES ITE WILLIAM E. GREENAWALT, OF DENVER, CO'IIORADO.

PROCESS OF EX'.I.RA('J'IING: METALS FROM THEIR ORES.

To all whom it may concern:

Be it known that I, WILLIAM E. GREENA- WALT, ing in Denver, in the county of Denver and State of Colorado, have invented certain new and useful Improvements in Processes of Extracting Metals from Their Ores, of which the following is a specification.

It has for its object the attainment of a practicable method of applying electrolysis by avoiding undue foul solutions, overcoming the anode and cathode difficulties, and the realization of pure deposited metal direct from the ore solvent.

So far as. I am aware, in the treatment of cupriferous ores by electrolytic methods, the electrolyzed and regenerated cathode solution, is returned to the ore. The solution may be electrolyzed with, or without, diaphragms, but in any case the solvent from which the copper has been electrolytically precipitated is returned to the ore, usually by first passing it through the anode compartment, if a diaphragm cell is used. In any event, with continuous operation the solution soonbecomes foul, and there follows as a result, decreased efliciency, im-

pure deposits, and a host of minor annoyances.

The conditions which have hitherto militated against electrolytic sulfate processes for the extraction of copper from its ores,

' are: (1) The insoluble anode. (2) Electrode inefliciency, due to useless oxidation and reduction. (3) Fouling of the electrolyte.

Up to the present time no really satisfactory anode for sulfate solutions has yet been devised. Lead is usually employed and has given the best average results. As ordinarily used, the lead oxidizes and disintegrates at an alarming rate, thereby uselessly increasing the electrical resistance, and asthe peroxid of lead becomes detached from the anode it drops to the bottom of the electrolyzer and short circuits the current, and has to be removed at frequent intervals at considerable expense. tions the. copper deposited at the cathode does not build up evenly, so that it becomes necessary to remove it at frequentintervals.

to avoid serious difliculties.

In the electrolysis of copper sulfate solutions resulting from leaching copper ores,

there is always present iron sulfate either Specification of Letters Patent.

a citizen of the United States, resid- Under Such condi-j Patented Apr. 18, 1916.

Application filed September 30, 1912. Serial No. 723,210.

i 1 cuso +greso u|-Fe (SO at the anode, 2-( 4)s i CuSOfi-QFeSO at the cathode,

and the original order of things has been reestablished without the current having accomplished any useful result. The efiiciency of any electrolytic process is mostly determined by the extent to which these secondary reactions take place. They can be largely avoided by maintaining a reasonably pure electrolyte. Ferrous sulfate, in the electrolyte, is not particularly harmful, but ferric sulfate, in contact with the cathode, is very deleterious.

The fouling of sulfate solutions has also presented a difficult problem. If a sulfate solution is used in a cyclic process, the impurities accumulate, thus making leaching and disposition more difficult, besides resulting in an impure copper. In my process the difliculties enumerated are entirely surmounted. Lead anodes are used, but the conditions under which they operate are such that oxidation and consequent disintegration of the lead is reduced to a minimum, and the disintegrated anode material is continuously and automatically removed from the electrolyzer. The deleterious cathode reactions do not take place, and the injurious fouling of the solutions is entirely avoided. In the treatment of the ore the copper is dissolved with a dilute solution of sulfuric acid, which results in the formation of a solution of cupric sulfate, containing small amounts of iron sulfate. The solution, after being filtered from the ore, is introduced into the cathode compartment of the electrolyz'er, while a slightly acidulated solution is introduced into the anode compartment. The anode solution may be the depleted cathode solution, but it will usually be the washwater from the ore after the richer copper sulfate solution hasbeen drained from it. Preferably, both the anode and cathode solutions are first saturated with sulfur dioxid before applying them to the electrolyzer.

When the current is turned on, copper is deposited at the cathode and acid regenerated at the anode;

3) CuSO,+H O+electric current: Cu+H SO,,

from which it will be seen that for every pound of copper deposited 1.54 pounds of sulfuric acid is regenerated. The diaphragm and a continually changing anolyte prevents the ferric sulfate from coming in contact with the deposited metal, and hence a high cathode efliciency is realized. This is also due largely to the fact that the iron in the solution is not cumulative, and hence the regeneration of the anolyte is mostly confined to the production of sulfuric acid.

In the operation of the process, while the copper is deposited on the cathode the regeneration of the solvent is confined to the anode, so that the catholyte, deprived of its copper and containing most of the impurities, may be wasted without perceptible loss,

while the anolyte, now rich in acid, is again applied to the ore. This method of procedure is facilitated on account of the large volume of electrolyte brought in contact with the cathode, which permits of so close an extraction of the copper that no tangible loss occurs in rejecting the catholyte. Similarly, the method of changing the anolyte, in contact with the anodes, is such that effective regeneration takes place, and in the presence of sulfur dioxid a large amount of excess acid is regenerated, so that the process is capable of an indefinite campaign, provided the consumption of acid is not too great.

The movement of the electrolyte is such that only a minimum amount of peroxid of' lead is formed, and this movement detaches the disintegrated anode material from the anode and entirely removes it from the cell. In this way the process may be worked automatically and continuously for one, or perhaps two, months, copper being deposited brought in contact with the anode, greatly diminishes the electromotive force required for the deposition of the copper and the regeneration of the acid, especially if sulfur dioxid is used as the depolarizer and acid generator. The anode solution will usually consist of washwater resulting from treating the ore with dilute acid. This washwater will usually be slightly acid and always contain considerable quantities of cupric sulfate. It may be further acidulated by saturating it with sulfur dioxid, derived from burning sulfur or from roasting sulfid ores. This serves three distinct purposes; First, to increase the conductivity of the electrolyte; second, to act as a depolarizer with a consequent diminution of the necessary voltage; third, as an acid generator. These advantages are very pronounced under the peculiar operation of my process.

When a solution of cupric sulfate is electrolyzed in the presence of sulfur dioxid in contact with the anode, sulfuric acid is formed according to the equation;

(4). CuSO,,|-SO +2H O:

Cu+2H,SO +7,300 calories.

oxid can be brought in contact with the anode at the moment of the liberation of the acid radical in combination with the copper sulfate, and this, in turn, will depend upon the current density and the method of doingit. In my process this reaction is very effectively carried out, and with a high efficiency, although it is not claimed that it can be 'done with theoretical exactness, but it is claimed that from 2 to 2.5 pounds of sulfuric acid can be regenerated for every pound of copper precipitated, and that the electromotive force to decompose the cupric sulfate will be reduced by fully 0.5 volt.

Having now discussed the general principles of the process, it will be more definitely described by referring to the accompanying drawing, in which 1 represents a leaching vat or agitator in which the ore is treated, say, with a sulfuric acid solution for the extraction of the copper. After the copper has been sufficiently dissolved, the resulting copper sulfate solution is filtered into storage tank 2 through the regulating valve 1*. The residue is then washed, and the washwater filtered into storage tank 3 through the regulating valve 1". Tank 2 now contains the rich copper sulfate solution, preferably neutralized or nearly so by the ore, and tank 3 contains the resulting washwater charged more or less with cupric sulfate, perhaps some free acid, and small amounts of the various salts from the ore. 7

' consists essentially of a cathode tank 31 containing the catholyte and the cathode 12.

9 is an anode bell suspended within the cathode tank, having a diaphragm 11, covering the lower portion of it, and containing the anolyte and the anodes 13. The anode bell is suspended by the hangers 14, which may be adjusted vertically, and oscillated by the mechanism 27. The anodes are suspended by the hangers32 and may be adjusted vertically;.they may also be given an oscillating motion, if desired, but this will usually not be necessary. The anolyte is exhausted from the electrolyzer through the..duct 10, and the catholyte through the duct 19.

23 is a sulfur dioxid generator communicating with the scrubbing towers by means of pipe 24; branch pipe 25 goes to tower 4 and branch pipe 26 to tower 5. The gas is exhausted from the generator and forced into the towers by means of the appara tus 33.

The bottom of the tower 4, through the trap pipe 6 communicates with the cathode compartment of the electrolyzer, while the bottom of tower 5, through the trap pipe 7 communicates with the anode compartment of the electrolyzer. The cupric sulfate solution from tank 2 is run into tower 4, the amount being regulated by the valve 2*, where, coming in contact with the sulfur dioxid, all salts are reduced to their lowest valencies with the simultaneous regeneration of a-certain amount of free acid, and the solution charged with the'gas. It then flowsintothe cathode compartment of the electrolyzer. Similarly the washwater is run in a regulated stream into tower 5, and after being charged with sulfur dioxid, flows into the anode compartment of the electrolyzer. Th e current is then turned on and the anode bell started to oscillate. Copper is deposited on the cathode and sulfuric acid regenerated at the anode, while at the same time a certain amount of oxygen is released, most of which escapes, but a very small amount peroxidizes the lead anodes. This peroxid, due to the oscillation of the anode bell is detached about as rapidly as formed and expelled from the electrolyzer with the anode solution, through the pipe or duct 10, which is flexible, into the tank 16, where the suspended peroxid is allowed to settle out of the anode solution. The clear regenerated anode solution, now freed from the peroxid, 1s pumped back to the leaching vat 1, where it acts on the copper in the ore. The duct 10, between the stationary cathode tank and the oscillatinganode bell,

is made flexible, so that thesolution may be withdrawn from the anode bell while oscillating and without mingling with the cathoyte.

The cathode solution is gradually deprived of its copper, and owing to the oscillating anode bell and diaphragm, it may be closely extracted, and deposited in a reguline condition to any thickness desired. If the cathode solution is quite impure, a dense diaphragm is used, in connection with a low current density, so that the difiusion of the anolyte to the catholyte may be as small as possible or avoided entirely. In this way practically all the copper in the catholyte may bedeposited on. the cathode and all the combined acid transferred to the anode. It is evident, therefore, that the catholyte,

I when impure, may be wasted without tangible loss, either of metal or acid. If however, the catholyte is not sufficiently impure to in any way interfere with the operation of the process, a dense diaphragm is not necessary, and if a small amount of diffusion occurs it will do no harm. In this case a thin diaphragm, which does not perceptibly increase the resistance of the current, is used, but it should be sufficiently tight to prevent any of the peroxid of lead from getting on the cathode. Under these conditions it will not be necessary to attempt close extraction of the copper from the catholyte, and when it is reduced to about one per cent., for example, it is flowed into tank 20 from whence it may be pumped back to the ore, or before pumping it back to the ore, itmay first be passed through the anode compartment of the electrolyzer to be augmented in acid. In any case, after being again applied to the ore, it may be used as the catholyte, if rich I in copper, or the anolyte, if it is desired to increase its copper content before electrolyzing to deposit the copper.

The sulfur 'dioxid in the catholyte serves two purposes; it reduces the harmful ferric salt to the harmless ferrous salt, and should any ferric salt diffuse through the diaand diaphragm greatly helps this reaction.

It is evident also, that the oscillation of the bell and diaphragm, brings in contact the sulfur dioxid with the oxygen at the moment of its liberation, in a very effective manner, and thus makes practicable an operation which has hitherto been of questionable utility.

After enough peroxid of lead has accumulated in tank 16 to warrant its reduction, it is taken out, washed, dried, mixed with carbon, and again reduced to metallic lead,

and again cast into anodes to pass through another cycle. In this way a certain amount of anode lead may last indefinitely, and pass through an indefinite number of cycles. If desired, or found necessary, brushes may be attached to the anode bell and oscillating diaphragm, to assist in removing the peroxid from the anode, and assist in forming a reguline deposit of copper on the cathode.

It is evident, in the process here described, that the impurities in the solution may be limited to the amounts found to do no appreciable harm, and this limit is best ascertained by direct experiment, and then the number of cells with dense diaphragms and low current density determined so that the amount of impure solution wasted will keep the remaining solution at the standard of purity desired.

It is also evident that the process may be applied to extraction of any metals from their ores. Although its application to the extraction of copper has been described in detail, it is in no way intended to limit its application to that metal. From the description given, its adaptability to other metals can readily be determined.

If the ore is a sulfid, and is roasted, copper sulfate may be formed in the roasting; the copper culfate so formed is equivalent to that produced by leachingwith acid. Similarly, the solvent may be ferric sulfate, in which case both sulfuric acid and ferric sulfate will be regenerated at the anode.

Having thus described my invention, what I claim is: 1. A process of extracting metals from their ores which consists in treating the ore with dilute sulfuric acid; separating the resulting rich metal sulfate solution from the .gangue and introducing it into the cathode compartment of an electrolyzer; Washing the residue and introducing the washwater into the anode compartment; then electrolyzing the solutions, whereby copper is precipitated at the cathode and the acid radical transferred to the anode, thus enriching the anolyte in acid; rejecting the cathode solution; returning the anode solution to the ore which in turnbecomes the metal solution to be electrolyzed as the catholyte while fresh washwater is used as the anolyte, and repeating this cycle of solution, precipitation and regeneration as often as necessary to get the desired results.

2. A process of extracting metals from their ores which consists in treating the ore with a solution of sulfuric acid; separating the resulting metal sulfate solution from the gangue; applying sulfur dioxid to the resulting metal solution and then introducing it into the cathode compartment of an electrolyzer; washing the residue, which results.

in an acidulated Water solution containing some metal sulfate; electrolyzing the metal sulfate solution as the catholyte and the washwater as the anolyte, whereby copper is preclpitated at the cathode and the anode cathode compartment of an electrolyzer;

washing the residue; applying sulfur dioxid to the washwater and introducing it into the anode compartment of the electrolyzer; electrolyzing the copper sulfate solution as the catholyte and the washwater as the anolyte whereby copper is deposited at the cathode and the anode solution enriched in acid; applying the anode solution, now enriched in acid, to the ore, which in turn becomes the metal solution and the catholyte, and repeating the cycle as often as necessary to get the desired results.

4;. A process of extracting metals from .their ores which consists in bringing the metals into solution as sulfate; filtering the resulting metal sulfate solution from the ore; applying sulfur dioxid to the filtered solution and then introducing it into the cathode compartment of an electrolyzer; washing the residue; applying sulfur dioxid to the washwater and introducing it ,into the anode compartment of the electrolyzer; electrolyzing the metal sulfatesolution as catholyte and the washwater as anolyte, whereby the metal is deposited at the cathode and the anode solution is enriched in acid; applying the anode solution, enriched in acid, to the ore which in turn becomes the metal sulfate solution and the catholyte, and repeating the cycle as often as necessary to get the desired results.

5. A process of extracting metals from their ores which consists in treating the ore to dissolve the metal as sulfate; separating themetal sulfate solution from the gangue; introducing the sulfate solution into the cathode compartment of an electrolyzer; Washing the residue and introducing the washwater into the anode compartment of an electrolyzer; electrolyzing the solutions to deposit the metal from the catholyte and regenerate acid in the anolyte; rejecting the depleted metal catholyte, and returning the washwater, now enriched in acid, to the ore to dissolve the metals, which then in turn becomes the catholyte.

6. In processes of extracting metals from their ores, the step Whichconsists in segregating a portion of the substantially neutral, foul metal sulfate solution and electrolyzing it as the catholyte, while using acidulated water as the anolyte; rejecting the electrolyzed and depleted cathode solu- 13o tion, and applying the anolyte enriched in acid, to the ore, which then becomes the metal solution and catholyte, and in this way maintaining a reasonably pure solution for the operation of the process.

7. In processes of extracting metals from their ores the step of maintaining a sufliciently pure working solution, which consists in segregating a certain amount of the foul metal sulfate solution; electrolyzing it as the catholyte and using acidulated solution of sulfur dioxid as the anolyte; rejecting the electrolyzed, foul, and depleted cathode solution, and applying the enriched acid anode solution to the ore.

8. A process of extracting metals from their ores which consists in dissolving the metals from the gangue, electrolyzing the resulting metal solution with insoluble anodes which are subject to disintegration, agitating the anolyte and catholyte, and catching the disintegrated anode material on the agitator.

9. A process of extracting metals from their ores which consists in dissolving the metals from the gangue, electrolyzing the resulting metal solution with insoluble anodes which are subject to disintegration, simultaneously agitating the anolyte and catholyte, catching the disintegrated anode material on the agitator, and removing the disintegrated anode material from the agitator with the electrolyte.

WILLIAM E. GREENAWALT.

Witnesses:

JOSEPH S. HEALEY, FRED L. Soo'r'r. 

